1. Field of the Invention:
This invention relates to the direct esterification of o-phosphoric acid with fatty alcohols, alkoxylated fatty alcohols and alkylphenol alkoxylates in the presence of a water entraining agent and at least one inorganic or organic base.
2. Statement of Related Art:
According to D. Sasse in "Houben-Weyl", Vol. 12, "Organische Phosphorverbindungen (Organic Phosphorus Compounds)", Part 2, page 143, the esterification of o-phosphoric acid with hydroxy compounds involves the formation of di- or polyphosphoric acids which then undergo alcoholic cleavage.
From Hollemann-Wiberg, "Lehrbuch der anorganischen Chemie", 83rd to 90th Edition, page 453, 1976, it is known for example that, at temperatures above 200.degree. C, o-phosphoric acid is converted with intermolecular elimination of water into diphosphoric acid which, in turn, changes via even higher polyphosphoric acids into metapolyphosphoric acid at temperatures above 300.degree. C with further elimination of water.
Since the primary reaction mainly takes place at temperatures of at least 170.degree. C., olefin is split off from the ester formed in a secondary reaction. Due to the relatively high vapor pressure of the olefins, the reaction temperature falls during the esterification and no more ester is formed.
The olefin formation is presumably the reason why no literature can be found on the direct esterification of fatty alcohols with o-phosphoric acid alone without the further use of phosphorus-containing substances.
U.S. Pat. No. 4,350,645 describes an esterification process using o-phosphoric acid. However, the o-phosphoric acid is not used on its own, but is used together with phosphorus pentoxide.
According to K. Sasse (loc. cit.), the reaction of a fatty alcohol with o-phosphoric acid proceeds up to an equilibrium in which the concentration of the ester formed is substantially proportional to the square of the concentration of the phosphoric acid. The establishment of the equilibrium is relatively quick in the case of lower alcohols, but rapidly decreases with increasing chain length of the aliphatic radical.